Electrical issue

[Jimmy B.]

As some of you know, I'm plane sitting for a friend. It is a 1983
172RG. Over the past couple of weeks, it seems to have picked up an
electrical issue. Occasionally, the "low voltage" light will flicker.
So far, I've seen this happen 3 times in about 5 weeks. Once, I
happened to be looking at the engine instrument panel when it happened
and both of the fuel gauges pegged to empty and then recovered during
the event. It happens so fast, if you are not looking at the panel when
it happens, you would miss it. So, I'm not sure how many times this has
happened without me knowing it.

Has anyone seen a similar problem and can point me in the right direction?

I already talked to a mechanic. His first thought was to continue
flying until the problem occurs and doesn't clear. (Basically wait
until it totally breaks.) I told him my concern about what this may be
doing to the avionics. (If the voltage is spiking low it could also be
spiking high.) After I explained this to him, he changed his tack and
said probably the first thing to do is to pull the cowling and check for
loose connectors, bad grounds, etc.

I'm just not sure how much I trust this guy.

[[email protected]]

On 26-Feb-2005, "Jimmy B." > wrote:

> I already talked to a mechanic. His first thought was to continue
> flying until the problem occurs and doesn't clear. (Basically wait
> until it totally breaks.) I told him my concern about what this may be
> doing to the avionics. (If the voltage is spiking low it could also be
> spiking high.) After I explained this to him, he changed his tack and
> said probably the first thing to do is to pull the cowling and check for
> loose connectors, bad grounds, etc.
>
> I'm just not sure how much I trust this guy.


I can see why his attitude is not inspiring confidence. However, it is
quite possible that he is right in thinking the problem might be a faulty
ground. The first thing I'd check would be the battery ground connection.
Could also be an intermittent master switch.

--
-Elliott Drucker

[Dan Luke]

"Jimmy B." wrote:
> As some of you know, I'm plane sitting for a friend. It is a 1983
> 172RG. Over the past couple of weeks, it seems to have picked up an
> electrical issue. Occasionally, the "low voltage" light will flicker.
> So far, I've seen this happen 3 times in about 5 weeks. Once, I
> happened to be looking at the engine instrument panel when it happened
> and both of the fuel gauges pegged to empty and then recovered during
> the event. It happens so fast, if you are not looking at the panel
> when it happens, you would miss it. So, I'm not sure how many times
> this has happened without me knowing it.
>
> Has anyone seen a similar problem and can point me in the right
> direction?

Oddly enough, this is may be a hydraulic problem. The symptoms you are
seeing are most likely from the voltage spike produced by the landing
gear hydraulic pump starting and stopping. The pump only needs to run
for a second to restore pressure. Both 172RGs I've flown (mine and a
renter) do it. I've only seen it on the takeoff roll, perhaps because
the hydraulic gear actuators unload as the weight comes off the wheels.

It's a problem only if it does it frequently, indicating a continual
loss of pressure from a leak of some kind.

For my own curiosity, what TAS do you get from that Cutlass at around
6,000'?
--
Dan
C172RG at BFM

[Jimmy B.]

wrote:
> On 26-Feb-2005, "Jimmy B." > wrote:
>
>
>>I already talked to a mechanic. His first thought was to continue
>>flying until the problem occurs and doesn't clear. (Basically wait
>>until it totally breaks.) I told him my concern about what this may be
>>doing to the avionics. (If the voltage is spiking low it could also be
>>spiking high.) After I explained this to him, he changed his tack and
>>said probably the first thing to do is to pull the cowling and check for
>>loose connectors, bad grounds, etc.
>>
>>I'm just not sure how much I trust this guy.
>
>
>
> I can see why his attitude is not inspiring confidence. However, it is
> quite possible that he is right in thinking the problem might be a faulty
> ground. The first thing I'd check would be the battery ground connection.
> Could also be an intermittent master switch.
>


Oh yeah, doing a solid connection check is a sound first step. I just
didn't like his "wait until it breaks" attitude. I didn't think of a
master switch. Good suggestion.

[Jimmy B.]

Dan Luke wrote:
> "Jimmy B." wrote:
>
>>As some of you know, I'm plane sitting for a friend. It is a 1983
>>172RG. Over the past couple of weeks, it seems to have picked up an
>>electrical issue. Occasionally, the "low voltage" light will flicker.
>>So far, I've seen this happen 3 times in about 5 weeks. Once, I
>>happened to be looking at the engine instrument panel when it happened
>>and both of the fuel gauges pegged to empty and then recovered during
>>the event. It happens so fast, if you are not looking at the panel
>>when it happens, you would miss it. So, I'm not sure how many times
>>this has happened without me knowing it.
>>
>>Has anyone seen a similar problem and can point me in the right
>>direction?
>
>
> Oddly enough, this is may be a hydraulic problem. The symptoms you are
> seeing are most likely from the voltage spike produced by the landing
> gear hydraulic pump starting and stopping. The pump only needs to run
> for a second to restore pressure. Both 172RGs I've flown (mine and a
> renter) do it. I've only seen it on the takeoff roll, perhaps because
> the hydraulic gear actuators unload as the weight comes off the wheels.
>
> It's a problem only if it does it frequently, indicating a continual
> loss of pressure from a leak of some kind.
>
> For my own curiosity, what TAS do you get from that Cutlass at around
> 6,000'?


I was reading the POH and it mentions that why the pump will cycle
during the take-off roll is because the nose gear squat switch
deactivates the power pack. So, when you lift the nose, the pump cycles
to repressurize the system, which has bled off a little sitting on the
ground.

Now that you mention it, last couple of times that I flew it, when I
pull the gear up the low voltage light comes on for a few seconds just
as the gear is completing the cycle.

Maybe I need to get the power pack overhauled? The one that is in there
is about 15 years old.

This one seems to cruise around 135 knots.

[Orval Fairbairn]

In article et>,
"Jimmy B." > wrote:

> Dan Luke wrote:
> > "Jimmy B." wrote:
> >
> >>As some of you know, I'm plane sitting for a friend. It is a 1983
> >>172RG. Over the past couple of weeks, it seems to have picked up an
> >>electrical issue. Occasionally, the "low voltage" light will flicker.
> >>So far, I've seen this happen 3 times in about 5 weeks. Once, I
> >>happened to be looking at the engine instrument panel when it happened
> >>and both of the fuel gauges pegged to empty and then recovered during
> >>the event. It happens so fast, if you are not looking at the panel
> >>when it happens, you would miss it. So, I'm not sure how many times
> >>this has happened without me knowing it.
> >>
> >>Has anyone seen a similar problem and can point me in the right
> >>direction?
> >
> >
> > Oddly enough, this is may be a hydraulic problem. The symptoms you are
> > seeing are most likely from the voltage spike produced by the landing
> > gear hydraulic pump starting and stopping. The pump only needs to run
> > for a second to restore pressure. Both 172RGs I've flown (mine and a
> > renter) do it. I've only seen it on the takeoff roll, perhaps because
> > the hydraulic gear actuators unload as the weight comes off the wheels.
> >
> > It's a problem only if it does it frequently, indicating a continual
> > loss of pressure from a leak of some kind.
> >
> > For my own curiosity, what TAS do you get from that Cutlass at around
> > 6,000'?
>
>
> I was reading the POH and it mentions that why the pump will cycle
> during the take-off roll is because the nose gear squat switch
> deactivates the power pack. So, when you lift the nose, the pump cycles
> to repressurize the system, which has bled off a little sitting on the
> ground.
>
> Now that you mention it, last couple of times that I flew it, when I
> pull the gear up the low voltage light comes on for a few seconds just
> as the gear is completing the cycle.
>
> Maybe I need to get the power pack overhauled? The one that is in there
> is about 15 years old.
>
> This one seems to cruise around 135 knots.


A couple of other possibilities:

1. Check for corrosion at the grounding points for the battery and for
the hydraulic pack.

2. Check for loose positive connections at the power pack and the main
bus bar,

3. Master solenoid could be dying (they do this).

[nrp]

> 3. Master solenoid could be dying (they do this).

I had to replace the Master solenoid on my 172M. Same type of
symptoms.

NRP

[Robert M. Gary]

I've been there done that. Sadly, no one on the list could ever predict
where such a problem can be. I ended up spending about $6,000 tracking
down the problem, replacing nearly everything in the electrical system.
In the end, it came down to replacing wires one at a time and cleaning
connections everywhere (especially ground). Electrical problems are the
worst!!

-Robert

[David Lesher]

"Robert M. Gary" > writes:

>I've been there done that. Sadly, no one on the list could ever predict
>where such a problem can be. I ended up spending about $6,000 tracking
>down the problem, replacing nearly everything in the electrical system.
>In the end, it came down to replacing wires one at a time and cleaning
>connections everywhere (especially ground). Electrical problems are the
>worst!!

Ouch, sorry to hear of your pain. But consider that the best step,
cleaning each connection, esp. the ground ones, is something an
owner can do her/himself [if it were legal; a question I'll skirt..]
investing only sweat equity....

One major reason for such nightmares may be the average A&P does
not have a lot of experience troubleshooting intermittent electrical
problems.

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433